What is HTML 5 all about?

HTML5 is a new version of HTML and XHTML. The HTML5 draft specification defines a single language that can be written in HTML and XML. It attempts to solve issues found in previous iterations of HTML and addresses the needs of Web Applications, an area previously not adequately covered by HTML.

Abstract

This specification defines the 5th major revision of the core language of the World Wide Web: the Hypertext Markup Language (HTML). In this version, new features are introduced to help Web application authors, new elements are introduced based on research into prevailing authoring practices, and special attention has been given to defining clear conformance criteria for user agents in an effort to improve interoperability.

The new standard incorporates features like video playback and drag-and-drop that have been previously dependent on third-party browser plug-inssuch as Adobe Flash, Microsoft Silverlight, and Google Gears.

Markup

HTML5 introduces a number of new elements and attributes that reflect typical usage on modern websites. Some of them are semantic replacements for common uses of generic block ( <div> ) and inline ( <span> ) elements, for example <nav> (website navigation block) and <footer> (usually referring to bottom of web page or to last lines of html code). Other elements provide new functionality through a standardized interface, such as the multimedia elements <audio> and <video> . Some deprecated elements from HTML 4.01 have been dropped, including purely presentational elements such as <font> , whose effects are achieved using Cascading Style Sheets. There is also a renewed emphasis on the importance of DOM scripting (e.g., JavaScript) in Web behavior.
The HTML5 syntax is no longer based on SGML despite the similarity of its markup. It has, however, been designed to be backward compatible with common parsing of older versions of HTML. It comes with a new introductory line that looks like an SGML document type declaration, which enables standards-compliant rendering in all browsers that use “DOCTYPE sniffing”.

New APIs

In addition to specifying markup, HTML5 specifies scripting application programming interfaces (APIs). Existing document object model (DOM) interfaces are extended and de facto features documented. There are also new APIs, such as:

The canvas element for immediate mode 2D drawing

Timed media playback

Offline storage database (offline web applications)

Document editing

Drag-and-drop

Cross-document messaging

Browser history management

MIME type and protocol handler registration

Microdata

Geolocation

Differences from HTML 4.01 and XHTML 1.x

The following is a cursory list of differences and some specific examples.

New parsing rules: oriented towards flexible parsing and compatibility; not based on SGML